The invention generally relates to oxygen concentrators, and more particularly relates to portable medical oxygen concentrators used by patients as a 24 hour a day source of supplemental oxygen.
Portable oxygen concentrators are becoming an increasingly desirable mode of supplying portable oxygen needs to patients requiring Long Term Oxygen Therapy (LTOT). These portable oxygen concentrators are replacing compressed gas cylinders and liquid oxygen systems, which have been the standard of care for many years. Replacing cylinders and liquid oxygen with a portable oxygen concentrator gives a patient the ability to travel onboard aircraft and avoid the requirement to return home to refill a liquid system or exchange empty cylinders. A particularly useful class of portable oxygen concentrators is designed to be used 24 hours a day, allowing users to move about and to travel for extended periods of time without the inconvenience of managing separate oxygen sources for home and portable use. These portable oxygen concentrators are typically in the range of 2 to 20 lbs and produce from 0.3 to 5.0 LPM of oxygen. Most of these portable concentrators are based on Pressure Swing Adsorption (PSA) or Vacuum Pressure Swing Adsorption (VPSA) designs which feed compressed air to selective-adsorption beds. In a typical oxygen concentrator, the beds utilize a zeolite adsorbent to selectively adsorb nitrogen, resulting in pressurized, oxygen-rich product gas.
The main elements in a typical portable therapeutic oxygen concentrator are shown in FIG. 1. Air is draw in, and typically filtered, at air inlet 1 before being pressurized by compressor 2 to a pressure of 1.2 to 2.5 atmospheres. The pressurized air is directed by a valve arrangement through adsorbent beds 3. An exemplary adsorbent bed implementation, used in a concentrator design developed by the inventors, is two columns filled with a lithium exchanged zeolite adsorbent in the ratio of about 1 gram of adsorbent per 1-5 ml of oxygen produced. The pressurized air is directed through these adsorber vessels or columns in a series of steps which constitute a gas separation cycle, often a PSA cycle or some variation including vacuum instead of, or in conjunction with, compression yielding overall compression ratios of about 1.5:1 to 4.0:1. Although many different arrangements of adsorber vessels and gas separation cycles are possible, the result is that nitrogen is removed by the adsorbent material, and the resulting oxygen rich gas is routed to a product gas storage device at 4. Some of the oxygen product gas can be routed back through the bed to flush out (purge) the adsorbed nitrogen to an exhaust 6. Generally multiple adsorbent beds, or columns in the exemplary device, are used so at least one bed may be used to make product while at least one other bed is being purged, ensuring a continuous flow of product gas. The purged gas is exhausted from the concentrator at the exhaust 6.
Such gas separation systems are known in the art, and it is appreciated that the gas flow control through the compressor and the adsorbent beds is complex and requires precise timing and control of parameters such as pressure, flow rate, and temperature to attain the desired oxygen concentration of 80% to 95% purity in the product gas stream. Accordingly, most modern concentrators also have a programmable controller 5, typically a microprocessor, to monitor and control the various operating parameters of the gas separation cycle. In particular, the controller controls the timing and operation of the various valves used to cycle the beds through feed and purge and pressure equalization steps which make up the gas separation cycle. Also present in most portable concentrators is a conserver 7 which acts to ensure that oxygen rich gas is only delivered to a patient during inhalation. Thus, less product gas is delivered than by means of a continuous flow arrangement, thereby allowing for smaller, lighter concentrator designs. A pulse of oxygen rich air, called a bolus, is delivered in response to a detected breath via the conserver. Using a conserver in conjunction with a gas concentrator may reduce the amount of oxygen required to maintain patient oxygen saturation by a factor of about 2:1 to 9:1 A typical concentrator will also contain a user/data interface 8 including elements such as an LCD display, alarm LEDs, audible buzzers, and control buttons. In addition to the above subsystems, most portable oxygen concentrators contain a rechargeable battery and charging system to power the concentrator while away from an AC or DC power source. These battery systems are typically composed of lithium ion cells and can power the concentrator from 2-12 hours depending on the amount of oxygen required by the patient and the capacity of the battery pack.
To be practical and usable by a individual needing therapeutic oxygen, portable oxygen concentrators should be less than about 2100 cubic inches and preferably less than 600 cubic inches in total volume, less than about 20 pounds and preferably less than 8 pounds in weight, and produce less than about 45 decibels of audible noise, while retaining the capacity to produce a flow of product gas adequate to provide for a patient's oxygen needs, usually a flow rate prescribed by a medical practitioner in about the range of 1 LPM to 6 LPM. Further, a portable medical oxygen concentrator must work under varied environmental and physical conditions without costly or frequent service or maintenance requirements and should be able to run for upwards of 20,000 hours before major maintenance is required, such as a compressor rebuild. Although fixed site PSA based concentrators have been available for many years, such fixed site units may weigh 30-50 pounds or more, be several cubic feet in size, and produce sound levels greater than 45 dBA. Thus portable concentrators involve a significant amount of miniaturization, leading to smaller, more complex designs compared to stationary units, yet they must remain relatively low cost to be available to a wide range of users. System size, weight, and complexity may lead to a necessarily higher degree of integration and design optimization. Moreover, the cost constraints of portable concentrators preclude the use of multiple pressure, temperature, and concentration sensors used by large scale industrial concentrators to help optimize efficiency. Significant teachings in concentrator art exist on just the subject of monitoring and control of various parts of the PSA process. Yet ultra-small portable concentrators have as much or greater need to accomplish such process control. A major required area of innovation in portable concentrator design is the need to accomplish the sort of process control practiced in large scale units without the luxury of the tools available to large scale system designers.
One particular challenge of portable concentrator design is that the devices are typically carried by the user. Since stationary oxygen concentrators are left in one site and the user uses a 50 ft tube extension to move about, the device is not nearly as close to the user under most circumstances. The portable oxygen concentrator must therefore be quieter, create less vibration, and be much more resilient to impacts, and function under constant movement and in various physical orientations.
Therefore, it is necessary to design a portable oxygen concentrator that incorporates an improved mechanical design that mitigates noise and vibration while simultaneously protects the device during impact. Prior art portable oxygen concentrators fail to meet all of these design criteria and as a result, the previously available products did not meet all the needs of the users and the home medical equipment providers. These prior art concentrators failed to meet the users' needs by being too large, too loud, and operated with too much vibration to be near the user 24 hours a day. These prior art concentrators similarly failed the equipment providers due to frequent malfunctions and short service lives. Some prior art portable oxygen concentrators may need a complete compressor rebuild after only 4000 hours, which equates to roughly six months of 24/7 usage. The portable nature of the equipment exposes the devices to being dragged over rough roads, bounced around in the trunks of cars, and knocked off counter tops to impact the ground from several feet. While some prior art equipment might hold up to these high levels of abuse, they do so with added weight and reduced performance parameters such as high noise levels or lowered oxygen flow rates.
Oxygen equipment used for Long Term Oxygen Therapy (LTOT) is optimally deployed for 3-5 years without any service requirements, but when there are service requirements or repairs, they must be able to be performed quickly and inexpensively. Prior art portable oxygen concentrators do not meet the objectives of fast and inexpensive repair in the event of damage. Many systems utilize adhesives to permanently bond parts together or have many components integrated into the outer housing such that replacing a damaged housing requires a nearly complete rebuild of the system. Not only do these assembly methods lead to more expensive repairs, but they limit the scope of facilities that can perform the repairs due to requirements for specific tooling and fixturing that common repair facilities would not have access to.